Screw pump or motor



June 2, 1953 M. B. SENNET 2,640,430

SCREW PUMP OR MOTOR Filed Sept. 24, 1949 s sheets sheet 1 FIG.

INVENTOR. MORGAN B. SENNET ATTORN YS,

June 2, 1953 M. B. sENNET SCREW PUMP 0R MOTOR Filed Sept. 24, I949 a sheets-slim 2 I l i I i mum IN VEN TOR.

U N m S 8 N m 0 M d, Z41 ATTORNE s.

June 2, 1953 M. B. SENNET SCREW PUMP 0R MOTOR 5 Sheets-Sheet 3 Filed Sept. 24, 1949 FIG. 3.

- INVENTOR. MORGAN B. SENNET ATORNYS.

Patented June 2, 1953 scmzw PUMP R MOTOR Morgan B. Sennet, Trenton, N.- J assignor to De Laval Steam Turbine Company, Trenton, N. J a corporation of New Jersey Application September 24, 1949, Serial No. 117,535

1 Claim. 7 (Cl. 103-128) This invention relates to a screw .pump or motor and particularly to a positive device of such type including a, plurality of intermeshing screws. In the following description, for simplicity, there will be referred to a pump; however, as will be obvious, the invention is equally applicable to a hydraulic motor of the multiple screw type.

Because of their ability to pump against large heads and operate at extremely high speeds, pumps of the type to which the invention relates have gone into widespread use. Generally speaking, such pumps involve a plurality of screws mounted within intersecting bores which provide a housing for the screw grooves and provide positive pumping action. Heretofore, it has been customary to provide housings in the form of single castings, or the like, which include not only the portions providing actual bearing for the screws but also the inlet and outlet chambers resulting in housings of considerable lengths. Such a construction has various disadvantages. First, the machining of the intersecting screw bores must be accomplished with boring bars which must extend through the space represented by either the inlet or the outlet chamber which necessarily must be large to avoid losses in the entrance or exit of the liquid to or from the screws. Difficulties are encountered in securing accurate boring under such conditions particularly when the bores which are required are of considerable length. The difliculties arefurther increased over ordinary boring by virtue of the fact that the boring cuts cannot be continuous because of the intersecting nature of the several bores.

Furthermore, the one-piece housing construction necessarily requires that the same material should be used to provide the immediate housing of the screws as is used for the remainder of the construction.

One of the objects of the present invention is theprovision .of ahousing for the screws which is independent of the major parts of the pump casing. By reason of the improved construction there is permitted an unlimited selection of materials for the housing immediately surrounding the screws, with the possibility that the casing may be made of less expensive material and of material more suited for the purpose. Furthermore, the housing of the screws need have a length only sufficient to provide the necessary enclosure required for securing a positive pump construction. The result of this is that shorter boring bars may be used which are, consequently, more rigid and result in more accurate machin ing of the bores. In brief, in accordance with the invention, the casing is made of two separate I relative arrangements of parts with the housing for the screws providing a third part having a flange which may be bolted or otherwise secured between the two portions of the casing. This construction offers another advantage in that using the same parts there is a freedom of provision of the relative directions in which the inlet and outlet passages may face, the same parts being adapted to be arranged in various angular positions with respect to each other, whereas in the previous construction entirely different casings had to be provided to change the relative directions of the passages just referred to. The two portions of the casing, furthermore, also require machining which is facilitated by making the two end portions of the casing of separate pieces. By virtue of the construction large inlet and outlet chambers result which are of primary importance in these screw pumps, especially at the inlet side so as to reduce to a minimum inlet losses and hence facilitate complete filling of the chambers which are provided by the intermeshing of the screws and the surrounding housing.

Furthermore, in accordance with the invention, it becomes possible to use idler screws of less length than heretofore, thereby reducing machining costs and insuring better accuracy for a given active length of the screw assembly.

The foregoing and other objects of the invention particularly relating to details of construc-- tion will become apparent from the following description, read in conjunction with the accompanying drawings, in which:

Figure 1 is a section through a pump embodying the invention, the section being taken on the broken surface the trace of which is indicated at l-l in Figure 3;

Figure 2 is a plan view of the pump illustrated in Figure 1;

Figure 3 is an end view looking at the lefthand end of Figure 1; and

Figure 4 is an end View looking at the righthand end of Figure 1.

The casing comprises the two parts 2 and 4 which may be cast of suitable material, these parts being provided with flanges 5 and 8 between which there is bolted by means of bolts and nuts I 4 and I6 the flange [2 of the separate screw housing [0 which, as will be evident, may be made of a material entirely different from that of the casing parts 2 and 4. The inboard part 4 may be provided with a suitable base l8. As will be evident from the symmetry of the construction the outboard part 2 may be rotated to various desired positions with respect to the part l, thus making possible various selected passages 44 and 48.

the inlet and outlet The screw-receiving bores are formed in the housing (0. As illustrated, there is a usual arrangement involving a single power screw meshing with a pair of idlers, each of the screws having two threads. As is known, in this type of pump this results in a positive pump when the housing is of sufiicient length to provide what is known as a closure. Under such conditions entirely closed chambers are formed by the screw threads and the housing so that the pump is of a positive type. It is, however, known that various other arrangements of screws may be used to provide positive pumping action, this being in accordance with the principles set forth in the patent to Montelius No. 1,698,802, dated January 15, 1929.

In the case of adoption of the particular screw arrangement just indicated the bores in the housing are such as indicated at 20, 22 and 24. In view of the fact that the housing is formed by a separate piece, it will be evident that for a given length of these bores the length of a boring bar may be minimum with the possibility of substantially increasing the accuracy of the machining involved.

The left-hand shaft extension 28 of the power screw 30 has a bearing at 26 in the casing part 2. The left-hand ends of the idler screws 32 and 34 have a thrust bearing provided at 33 by a radial surface inside the casing part 2. While under running conditions the idler screws will be thrust toward the left in Figure 1, provision is made to limit their movement in a, right-hand direction by cast lugs 38 which project in position to be engaged by their right-hand ends.

Inlet and outlet chambers 42 and E5 are provided communicating respectively with the inlet and outlet passages 44 and 48. It will be noted that these chambers 42 and 46 in the present construction are quite large and provide free entrance and exit of the liquid being pumped to and from the screws.

A ball-bearing 50 provides the mounting for the right-hand shaft extension 5| of the power screw 30, this bearing being held in position by means of the cover 52 bolted to the casing part l. By the use of the ball-bearingit is possible to accommodate substantially greater side thrust on the power rotor than by the constructions heretofore used; furthermore, by the use of the ballbearing the axial unbalance of the power rotor may be taken care of without resorting to a. balancing piston with the necessary leakoff holes which are expensive to produce. Furthermore, not only is difiiculty encountered in the drilling of long holes through the power rotor but such drilling substantially weakens the shaft,

Instead of using conventional packing a mechanical seal arrangement, indicated generallyat 54, is provided to keep the pumped fluid from the chamber housing the ball-bearing. This mechanical seal is of known construction and forms no part of the present invention. Briefly, it comprises a synthetic rubber seat ring 50 supporting a floating seat 58 on which bears the sealing washer 60 of carbon rotating with the shaftand rim in tight engagement with the floating seat as by the action of a construction including a spring 62 backed up by a washer 64 which bears'against the right-hand end of the power screw.

The major advantages of the improved construction discussed heretofore will now be evident. In addition to the advantages a d y using the separate housing, namely, f tages of more accurate machining, th posslblhty of adopting any desired material for the housing, and the provision of free inlet and outlet chambers, it will be noted that the idler screws need not extend toward the right in Figure 1 substantially beyond the right-hand end of the housing [0. In constructions heretofore adopted these idler screws generally had to extend further toward the right to come into close relationship with the right-hand walls of the discharge chamber in order to provide limitation of their righthand movements. The lugs 38 efiectively limit the right-hand movement of the idlers and at the same time do not appreciably reduce the free space at the right-hand ends of these idlers, so that the discharge of the liquid being pumped is not impeded. As compared with previous constructions, the overall length of the improved pump is substantially less.

It may be noted that in the use of a similar construction as a motor the passage 48 would be the inlet passage for :the liquid and the passage M would be the outlet passage. As will be evident, the same advantages would be secured in the case of such a motor.

It may also be noted that the various advantages of the present invention will result if the screw pump or motor is of a non-positive type such as may be provided by departing from the particular rotor arrangements specified in said Montelius patent for positive devices. For ekample, a non-positive pump or motor may be provided by utilizing a power'screw having two threads in combination with three or four idlers, each of which has two threads. Other combinations of screws may equally well be used for the attainment of pumps or motors having various characteristics.

What is claimed is:

A screw device of the type described comprising a housing element provided with a plurality of intersecting bores, intermeshin screws mounted within said bores, a pair of easing elements separate from said housing element and having walls spaced from the housing element to provide inlet and outlet chambers for free entrance and exit of fluid at the-ends of said bores, said housing element being provided with an external flange secured between said casing elements, said flange being located approximately at the central portion of said housing element, a bearing mounted in one of said casing elements for one of said screws, and a seal for isolating said bearing from the adjacent one of said chambers, one of said casing elements being provided with a lug to limit endwise movement of at least one of said screws in" a direction towards the high pressure end'ther-eof, and the other of said casing elements providing a surface receiving end thrust of at least one of said screws.

MORGAN B. SENNET.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 630,648 Brewer Aug. 8, 1899 1,233,599 Nuebling July 17, 1917 2,079,083 Montelius May 4, 1937 2,193,671 Dolza Mar. 12, 194.0 2,381,695 Sennet Aug. 7, 1945 FOREIGN PATENTS Number Country Date 430,601 Great Britain June 21, 1935 

